Peoria, Ill. (WMBD) – Central Illinois is expected to experience a volatile winter featuring large temperature swings and an active storm track. This pattern will be driven by a moderate to strong La Niña in the eastern Pacific Ocean, but snow lovers may be disappointed.
- Moderate to strong La Niña conditions expected through the winter and will trend weaker in the Spring
- Above average temperatures and above average precipitation is expected
- Despite above average precipitation, snowfall is expected to be below average
My prediction for a warmer and wetter winter is largely based on the strength of the La Niña conditions. La Niña’s are highly variable and the end results are often driven by shorter term climate patterns called Teleconnections.
Lets breakdown the various teleconnections and discuss how they will impact our local weather
The El Niño Southern Oscillation (ENSO)
It’s often highlighted in seasonal forecasts such as this to help determine how the weather across the U.S. will be impacted. There are three phases to ENSO that are determined by monitoring sea surface temperatures and wind patterns over the Pacific Ocean.
- El Niño (Positive Phase) – This phase occurs when sea surface temperatures across the central and eastern Pacific are above average. This often results in less rainfall over Indonesia and increased rainfall across the central and eastern Pacific. Shifting winds near the equator will carry tropical moisture north into North America. This typically leads to cooler and wetter seasons across the southern U.S. while warmer and drier seasons occur across the northern U.S.
- La Niña (Negative Phase) – In this phase, sea surface temperatures across the central and eastern Pacific are below average and rainfall often increases across Indonesia. The sub-tropical jet stream weakens and polar jet becomes the main driving force for storms across the U.S. and results in dry and warm conditions across the southern U.S. while the northern part of the country sees cooler and wetter seasons.
- Neutral Phase – Sea surface temperatures across the central and eastern Pacific Ocean are near average and there for “neutral”. While the direct impacts of this phase are often minimal, warm and wet conditions typically prevail in the southeast U.S. while colder conditions linger across the northern U.S.
The Arctic Oscillation (AO)
The Arctic Oscillation is a short term teleconnection that determines how much cold air will impact the eastern U.S. Unlike ENSO, the predictability of the Arctic Oscillation only extends a few weeks out. The phase of the AO is characterized by the strength of the winds circulating counterclockwise around the north pole, a phenomenon known as the Polar Vortex.
- Positive Phase – This phase of the AO indicates that the Polar Vortex is strong. This produces stronger westerly flow around the Arctic which confines colder air to the Arctic Circle.
- Negative Phase – The Polar Vortex is in a weakened state and the jet stream becomes highly amplified and sends arctic air south. In Central Illinois, a negative phase of the AO often results in more frequent arctic air masses and increased storminess making for some rather uncomfortable stretches of winter weather.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation is based on sea-level pressure difference between the Azores High and the Subpolar Low. Similar to the AO, the NAO is only predictable a few weeks out.
- Positive Phase – This phase of the NAO means that there is a significant difference in pressure between the Azores High and the Subpolar Low, in other words, both the high and the low are strong. This makes the jet stream winds over the north Atlantic more westerly which then leads to warmer temperatures across the eastern U.S.
- Negative Phase – The NAO is in this phase when the difference in pressure between the Azores High and the Subpolar Low is small and both systems are weak. This leads to a wavier jet stream and a blocking ridge over Greenland. This leads to warmer temperatures pushing north towards the North Pole over the Atlantic while colder temperatures move southward over the eastern U.S.
As previously mentioned La Niña winters are often highly variable and are full of large temperatures swings and pattern changes. This high variability is largely due influences from the Arctic Oscillation and the North Atlantic Oscillation. For instance, for the past few weeks the AO and the NAO have both been in a positive phase. This has lead to relatively mild temperatures across the eastern U.S. When both patterns shift into a negative phase, Arctic air will plunge southward. These arctic blasts are particularly strong during La Niña winters given the upper level flow is typically conducive for colder than normal temperatures across the northern U.S.
While these teleconnections will have impacts on our week to week weather patterns, strong La Niña events have historically lead to warmer than normal temperatures across the Midwest during winter.
My Bold Prediction
As always there will be periods of cold and snow and periods of sun and warmth. We are bound to experience some powerful storms that will bring rain, ice and heavy snow to the area, after all it’s Illinois. However, when it’s all said and done, I think we have some identifiable trends at the end of February. Here are my expectations…
Temperature Outlook – Warmer than average
My forecast largely leans towards the historical averages of a strong La Niña which favors warmer temperatures across much of the U.S. This is a solution that also seems to be favored by recent seasonal model predictions. That’s not to say it won’t get cold, it most certainly will, but by the end of winter I suspect that more often than not our temperatures would have been above average.
Precipitation Outlook – Wetter than average
This portion of the forecast was largely based on typical La Niña expectations and seasonal model predictions. I have some concern that ongoing drought conditions across Central Illinois could act to limit moisture, but feel that these conditions are temporary and will be alleviated in the coming weeks.
To be honest, there’s no scientific basis for a seasonal snowfall prediction so your guess is as good as mine. That said I’ll take stab at it and give you my prediction and reasoning.
Below average snowfall (15 to 23 inches)
Peoria averages about 24 inches of snow in a winter season. The past three winters (2017, 2018 and 2019) all experienced above average snowfall with 32.1″, 36.4″ and 35.9″ respectively. The past two winters were off to an early start and saw decent snow in the month of January.
This year, despite having a trace of snow on October 26th, we have yet to see any measurable snow this season. That’s not all that unusual, the average date of our first measurable snowfall is November 23rd while the average date of our first one inch snowfall is December 11th. However, I feel storm systems will generally pass west of the Mississippi River this winter which would keep us on the warmer side of these storm systems. That’s not to say it won’t snow, it certainly will, but I think the heavier snows will remain to our north and west. This storm track and the expected warmer temperatures allow be to believe we will experience below average snowfall.